Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$114.59	5.265%	$120.6232	$120.62	$120.60	$120.60
Purchase #2	$95.34	5.388%	$100.4769	$100.48	$100.50	$100.50
Purchase #3	$37.80	6.487%	$40.2521	$40.25	$40.25	$40.30
Purchase #4	$212.74	7.131%	$227.9105	$227.91	$227.90	$227.90
Purchase #5	$113.82	11.323%	$126.7078	$126.71	$126.70	$126.70
Purchase #6	$170.85	5.576%	$180.3766	$180.38	$180.40	$180.40
Purchase #7	$38.61	11.513%	$43.0552	$43.06	$43.05	$43.10
7 purchase totals =	$783.75		$839.4023	$839.41	$839.40	$839.50